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potential are often enormous. Great variation is shown in the 
direction and character of the discharge. n examination of a 
living tree as a conductor reveals the fact that the portions con- 
taining the greatest proportion of starch, glucose, or other sugars 
greatest resistance. In consequence lightning discharges gener- 
ally pass through a tree trunk in the growing layers and sap wood, 
and the actual amount of mechanical lesion accomplished will 
depend upon the size of the discharging spark, or flash. A more 
or less constant discharge is constantly taking place through trees 
but it is only when the difference in potential becomes very great 
that a lightning stroke results. 
he increasing attention paid to origin of forest fires has led to 
indubitable proof that their origin is often to be traced to flashes 
of lightning. The following example has come under the author's 
observation. While in camp on Minard’s Bay on the western side 
of Priest Lake, Idaho, in 1900 in company with Mr. Sam Davis, 
a forest ranger detailed for duty in that portion of the reserve, a 
number of severe thunderstorms occurred. One morning we 
were warned by a boatman from the opposite side of the lake that 
lightning had been seen to strike a tree up on the mountain side, 
back from the lake, the night before. The lesser mountain ridge 
was climbed in about three hours’ hard work, and then favorable 
positions were secured from which the forested slopes around the 
lake could be observed. After a time our watch was rewarded 
by the sight of puffs of smoke from a point two miles away. On 
making our way to this place the base of a pine tree, and a widen- 
ing circle of leaves and humus were found to be burning briskly. 
A flash of lightning had struck the top of the pine tree and after 
coming down it for thirty feet had jumped to the top of a dead 
spruce leaning against the pine, setting fire to a portion about 
six feet in length. This top of the spruce had been burned away 
from the trunk and the blazing fragment had then fallen to 
the ground against the base of the pine, which was partly rotted 
and dry. At the time it was discovered, this incipient forest fire 
had eaten its way into the heart of the pine tree, and outwardly 
